N-terminally tagged prion protein supports prion propagation in transgenic mice

Abstract

The eight amino acid sequence, Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys, representing the FLAG peptide, was inserted after codons 22 or 88 of the mouse (Mo) prion protein (PrP) gene. Inclusion of the FLAG sequence at these locations interfered neither with the cellular processing of PrP(C) nor its conversion into PrP(Sc). Inclusion of the FLAG epitope at residue 22 but not at residue 88 facilitated immunodetection of tagged PrP by anti-FLAG monoclonal antibodies (mAbs). Inoculation of transgenic (Tg) mice expressing N-terminally tagged MoPrP with Mo prions resulted in abbreviated incubation times, indicating that the FLAG sequence was not deleterious to prion propagation. Immunopurification of FLAG-tagged MoPrP(C) in the brains of Tg mice was achieved using the calcium-dependent anti-FLAG M1 mAb and non- denaturing procedures. Although the function of PrP(C) remains unknown, our studies demonstrate that some modifications of PrP(C) do not inhibit the one biological activity that can be measured, i.e., conversion into PrP(Sc). Tagged PrP molecules may prove useful in the development of improved assays for prions as well as structural studies of the PrP isoforms.